This is signals/signal_functions.c (Listing 20-4, page 408), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

This page shows the "distribution" or "book" version of the file (why are there two versions?), or the differences between the two versions. You can switch between the views using the tabs below.

In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.

  Cover of The Linux Programming Interface
+/* signal_functions.c
+   Various useful functions for working with signals.
 #define _GNU_SOURCE
 #include <string.h>
 #include <signal.h>
 #include "signal_functions.h"           /* Declares functions defined here */
 #include "tlpi_hdr.h"
 /* NOTE: All of the following functions employ fprintf(), which
    is not async-signal-safe (see Section 21.1.2). As such, these
    functions are also not async-signal-safe (i.e., beware of
    indiscriminately calling them from signal handlers). */
 void                    /* Print list of signals within a signal set */
 printSigset(FILE *of, const char *prefix, const sigset_t *sigset)
     int sig, cnt;
     cnt = 0;
     for (sig = 1; sig < NSIG; sig++) {
         if (sigismember(sigset, sig)) {
             fprintf(of, "%s%d (%s)\n", prefix, sig, strsignal(sig));
     if (cnt == 0)
         fprintf(of, "%s<empty signal set>\n", prefix);
 int                     /* Print mask of blocked signals for this process */
 printSigMask(FILE *of, const char *msg)
     sigset_t currMask;
     if (msg != NULL)
         fprintf(of, "%s", msg);
     if (sigprocmask(SIG_BLOCK, NULL, &currMask) == -1)
         return -1;
     printSigset(of, "\t\t", &currMask);
     return 0;
 int                     /* Print signals currently pending for this process */
 printPendingSigs(FILE *of, const char *msg)
     sigset_t pendingSigs;
     if (msg != NULL)
         fprintf(of, "%s", msg);
     if (sigpending(&pendingSigs) == -1)
         return -1;
     printSigset(of, "\t\t", &pendingSigs);
     return 0;

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